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Publication numberUS5533400 A
Publication typeGrant
Application numberUS 08/117,918
Publication dateJul 9, 1996
Filing dateSep 9, 1993
Priority dateSep 4, 1992
Fee statusLapsed
Also published asDE4229340A1, DE4229340C2, DE59304871D1, EP0585623A2, EP0585623A3, EP0585623B1
Publication number08117918, 117918, US 5533400 A, US 5533400A, US-A-5533400, US5533400 A, US5533400A
InventorsRobert Gasch, Mingfu Liao
Original AssigneeCarl Schenck Ag
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Process for the early detection of a crack in a rotating shaft
US 5533400 A
Abstract
The present invention relates to a process for the early detection of a crack in a rotating shaft, particularly in a shaft of a turbo generator used in a power plant. Signals that represent flexural vibrations of the shaft are measured--as a function of the rotational angle, continuously or at time intervals by means of vibration sensors in at least two radial, preferably perpendicular, directions with respect to each other. These signals are transmitted to a signal processor which uses the signals to ascertain the harmonic vibration components with single and/or double and/or triple rotational frequencies and then the processor forms single and/or double and/or triple rotational-frequent vibration orbits by means of a vectorial combination of these vibration components.
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Claims(2)
What is claimed is:
1. A process for the early detection of a crack in a rotating shaft, in which signals representative of flexural vibrations of the shaft are picked up as a function of rotational angle by means of vibration sensors in at least two radial directions, and the signals are transmitted to a signal processor which uses the signals to ascertain the harmonic vibration components with at least a single rotational frequency and then the processor forms at least a single rotational-frequent vibration orbit by means of a vectorial combination of the vibration components, the improvement comprising in that the signal processor vectorially decomposes at least the single rotational-frequent vibration orbit formed on the basis of the harmonic vibration components into a forward whirl turning in the same rotational direction as the shaft and into a backward whirl turning in the opposite direction to the rotation of the shaft and in that the backward whirl is compared with a reference base-line ascertained in one of the new and normal states.
2. A process for the early detection of a crack in a rotating shaft, in which signals representative of flexural vibrations of the shaft are picked up as a function of rotational angle by means of vibration sensors in at least two radial directions, and the signals are transmitted to a signal processor which uses the signals to ascertain the harmonic vibration components with at least a single rotational frequency and then the processor forms at least a single rotational-frequent vibration orbit by means of a vectorial combination of the vibration components, the improvement comprising in that the signal processor vectorially decomposes at least the single rotational-frequent vibration orbit formed on the basis of the harmonic vibration components into a forward whirl turning in the same rotational direction as the shaft and into a backward whirl turning in the opposite direction to the rotation of the shaft and in that the backward whirl is compared with a reference base-line ascertained in one of the new and normal states, and wherein acceleration pick-ups are utilized as the vibration sensors positioned in one rotational plane and spaced apart by 90 with respect to each other along the circumference of the shaft, and the signals of the acceleration pick-ups are transmitted to the signal processor via a telemetric device.
Description
BACKGROUND OF THE INVENTION

The present invention relates to a process for detecting cracks in rotating shafts.

The early detection of a crack in a shaft is particularly important in the case of large machines of the type used in power plants since this prevents damage to such machines as well as the associated costs and the risks. Since these machines are often in continuous operation for prolonged periods of time and since it is not economically feasible to temporarily take them out of operation, processes have already been developed in which, by means of continuous monitoring and analysis of the flexural vibrations in the shaft, an attempt is made to detect the presence of a crack in the shaft on the basis of certain changes in the vibration.

Thus, U.S. Pat. No. 4,380,172 discloses a process for determining cracks in a turbine rotor in which the vibrations of the rotor are picked up and evaluated during the operation of the turbine under load as well as at an essentially normal operating speed. For this purpose, there are vibration sensors positioned at 90 with respect to each other along the circumference of the bearings, and these sensors can be designed as displacement or acceleration pick-ups. These vibration signals are first picked up when the turbine is in its normal operation, processed and then the harmonic components of the vibration signals are determined by means of signal analyses. As a result, the vibration components appear with single, double and triple rotational frequencies. In order to detect cracks as soon as possible on the basis of an evaluation of these vibration components, the temperature of the turbine rotor is changed, for example, by means of an appropriate regulation of the steam temperature, as a result of which thermal stresses are temporarily created in the rotor which, in turn, influence the crack-related vibration behavior of the rotor. The existence of a crack is ascertained by comparing the vibration signals picked up and analyzed before and after the temperature change, and particularly by observing the change of their two-fold rotational-frequent components. The known process, however, has proven to be insufficiently informative since unbalance, alignment errors, bearing damage and innumerable other influences can give rise to vibration phenomena which are similar to the vibration phenomena due to a crack. Field experiments have showed that the evidence of a crack can be hidden by the simultaneous occurrence of various disturbances. It was also observed that two-pole generators excite two-fold rotational-frequent vibrations in connection with rotational-frequent variations without the presence of a crack.

In order to distinguish vibration characteristics of a shaft crack from other function disturbances which result in a similar vibration behavior, it is a known process to form the kinetic shaft orbit or shaft-vibration orbit on the basis of the picked-up signals and to then represent and evaluate these signals in a polar diagram. It is also a known process to represent and evaluate the formation of vibration figures of the filtered-out vibration component with double rotational frequency. The evaluation of the vibration figures, however, calls for a number of additional analyses, as a result of which it is very complex and expensive. There are no provisions for a decomposition of the vibration figures into forward and backward whirls.

SUMMARY OF THE INVENTION

The invention is based on the objective of creating a process of the above-mentioned type for purposes of the early detection of a crack in a rotating shaft, a process which makes it possible to analyze the vibrations picked up during operation in order to clearly distinguish between vibrations stemming from a crack and vibrations resulting from other causes.

According to the invention, this objective is achieved in that the signal processor vectorially decomposes the rotational-frequent and/or double rotational-frequent and/or triple rotational-frequent vibration orbits formed on the basis of the harmonic vibration components into forward whirls turning in the same rotational direction as the shaft and into backward whirls turning in the opposite direction to the rotation of the shaft, and in that the backward whirl is compared with a base-line information ascertained in the new or normal state.

The process according to the invention is based on the knowledge that, in the ascertained vibration orbits, the tracks of forward and backward vectors overlap and these tracks are affected differently by the occurrences which excite the vibrations. In this context, it has been surprisingly found that, in addition to the forward rotational-frequent, double rotational-frequent and triple rotational-frequent vibrations, the shaft crack especially strongly excites the backward rotational-frequent vibration, which is not significantly affected by other excitation resources (unbalance, uneven shaft stiffness). By observing and comparing the rotational-frequent, double rotational-frequent or triple rotational-frequent backward whirls with an appropriate reference base-line ascertained in the new or normal state, it becomes possible to ascertain at an early point in time and with a certainty unknown until now whether a crack has formed in the shaft and the extent to which an existing crack is changing. In this manner, the process according to the invention greatly improves the resolution of the very complex contents of the measured signals when it comes to the early detection of shaft cracks.

The process according to the invention is particularly well-suited for the continuous monitoring of the state of the shaft motion of power plant machines such as turbo generators, generators, cooling water pumps and the like, all of which are operated continuously over prolonged periods of time at the same speed. Here, it is often the case that the operating speed lies in the supercritical rotational range, in which the crack-related vibration fraction is very small, especially with respect to the double- and triple-rotational vibrations, and thus difficult to detect. In order to overcome this disadvantage, another embodiment of the invention proposes that, as vibration sensors, acceleration pick-ups are positioned in one rotational plane and staggered by 90 with respect to each other along the circumference of shaft. The signals of the acceleration pick-ups are transmitted to the signal processor via a telemetric device. The arrangement of acceleration pick-ups on the shaft considerably improves the resolution of the vibration measurement, so that even smaller signals can be better resolved and crack responses can be better recognized.

BRIEF DESCRIPTION OF THE DRAWINGS

Novel features and advantages of the present invention in addition to those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

FIG. 1 is a simplified schematic view of a shaft with apparatus for carrying out the process of the present invention;

FIG. 2 is a diagrammatic view illustrating the vectorial combination of the detected vibrations forming a wave-vibration diagram;

FIG. 3 is a spatial representation of circular and elliptic vibration diagrams of single, double and triple rotational frequencies as a function of shaft speed; and

FIG. 4 is a diagrammatic view illustrating the vectorial decomposition of a vibration orbit into forward and backward whirls.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a shaft 1 which is rotatably supported in bearings 2, 3. Attached to the shaft 1 is a phase transmitter 11 which transmits a reference signal to a signal processor 7. Piezo-electric acceleration pick-ups 4, 5 are arranged on the shaft 1 in a common rotation plane at an angle of 90 from one another. By means of a telemetric device 6, the voltage signals of the acceleration pick-ups 4, 5 are transmitted to the signal processor 7 where they are amplified and filtered in a manner suitable for further processing. The processed voltage signals are transmitted together with the signal of the phase transmitter 11 to an electronic signal processor 8 where the signals are processed in a manner more fully described below. The data obtained on the basis of the signal processor 8 can be entered into a memory 9 and displayed by means of a monitor 10.

FIG. 2 shows examples of acceleration signals b1, b2 as a function of time t, and, on the basis of the flexural vibrations present in shaft 1, these signals are picked up by the acceleration pick-ups 4, 5 while the shaft 1 is rotating. The acceleration signals reflect directly the vibrations of the shaft 1. The vectorial addition of signals b1 and b2 makes it possible to form a vibration orbit K which is traversed rotationally in the turning direction of shaft 1. Thus, vibration orbit K describes the kinetic shaft orbit traversed about the shaft mid-point at a certain operating state.

Comparable vibration orbit can also be formed by the harmonic vibration components of each measured vibration of the shaft. The diagram according to FIG. 3 shows examples of vibration orbits of single, double and triple rotational-frequent harmonic vibration components over the shaft speed Ω. In this context, the speed Ω is expressed as the ratio of the absolute speed to the critical speed. The representation shows that the rotational-frequent vibration has its greatest amplitude at the critical speed, while the double rotational-frequent vibration has its greatest amplitude at half the critical speed. The triple rotational-frequent vibration has its greatest amplitude at one-third of the critical speed. If the operating state lies in the supercritical range, there are very small amplitudes and correspondingly small signals, especially for the harmonic vibration components with double and triple rotational frequencies. In accordance with the process according to the invention, vibration orbits corresponding to the representation in FIG. 3 are formed by means of the analysis of the vibration signals picked up at the operating speed of the shaft, after which these signals are decomposed into forward whirls and backward whirls by means of vectorial decomposition. FIG. 4 shows an example of this vectorial decomposition with reference to a rotational-frequent synchronously traversed slim ellipsis of a first harmonic vibration component. The elliptic vibration orbit S originates from the superimposition of forward and backward circular whirls. The vectorial decomposition of the vector R which generates the vibration orbit S makes it possible to determine the forward whirl R+1 and the backward whirl R1. The backward whirl R-1 is compared with a comparable reference base-line which is stored in the memory 9 and which is ascertained in an analogous manner in the normal or new state of the machine. A positive deviation is an indication of the presence of a crack in the shaft being monitored. Once a crack has been found, it is possible to track the growth of the crack according to the increase of the backward whirl.

Essentially, the rotational-frequent backward whirl of the first harmonic generally is a sufficiently clear indicator for the early detection of cracks in accordance with the process according to the invention, especially since the component's higher signal strength allows a better resolution. According to the inherent vibrational behavior of the entire rotor arrangement, the features of the disturbance vibrations which overlap the crack response and the operating speed present, it is advantageous to also observe the behavior of the backward whirls of the vibration orbits with double and triple rotational frequencies in order to obtain a more informative conclusion on the presence of a crack.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US4380172 *Feb 19, 1981Apr 19, 1983General Electric CompanyOn-line rotor crack detection
US4464935 *May 9, 1983Aug 14, 1984General Electric CompanyShaft vibration evaluation
US4751657 *Jul 8, 1985Jun 14, 1988General Electric CompanyMethod and apparatus for detecting axial cracks in rotors for rotating machinery
US5086775 *Nov 2, 1990Feb 11, 1992University Of RochesterMethod and apparatus for using Doppler modulation parameters for estimation of vibration amplitude
US5099848 *Nov 2, 1990Mar 31, 1992University Of RochesterMethod and apparatus for breast imaging and tumor detection using modal vibration analysis
DE4012278A1 *Apr 17, 1990Oct 18, 1990Hitachi LtdDiagnostic system for installations with special operating conditions - uses neural network model for efficient, objective diagnosis
DE4110110A1 *Mar 27, 1991Oct 2, 1991Nissan MotorPruefverfahren und -vorrichtung fuer brucheinleitung
Non-Patent Citations
Reference
1 *Fertigungsmebtechnik, Wolfgang Dutschke, B. G. Teubner Stuttgart 1990,S.93; 4Abs. von untern.
2 *ShaftCrack Detection, Methodology 1988, 16 Seiten Firmenschrift der Bently Nevada Corp. Minden/Nevada.
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US6065344 *Nov 27, 1998May 23, 2000General Electric Co.Apparatus and methods for cooling an ultrasonic inspection transducer for turbine rotor wheel repair
US6098022 *Oct 17, 1997Aug 1, 2000Test Devices, Inc.Detecting anomalies in rotating components
US6116089 *Aug 7, 1997Sep 12, 2000Reliance Electric Technologies, LlcMethod and apparatus for identifying defects in a rotating machine system
US6234022 *Aug 12, 1999May 22, 2001Nsk Ltd.Bearing rigidity evaluation apparatus
US6289735 *Sep 29, 1998Sep 18, 2001Reliance Electric Technologies, LlcMachine diagnostic system and method for vibration analysis
US6346807Oct 22, 1999Feb 12, 2002Bently Nevada CorporationDigital eddy current proximity system: apparatus and method
US6449564Nov 23, 1998Sep 10, 2002General Electric CompanyApparatus and method for monitoring shaft cracking or incipient pinion slip in a geared system
US6456945Jul 5, 2000Sep 24, 2002Test Devices, Inc.Detecting anomalies in rotating components
US6664782Jan 8, 2002Dec 16, 2003Bently Nevada, LlcDigital eddy current proximity system: apparatus and method
US6705168Feb 12, 2003Mar 16, 2004Ol Db Acoustics & VibrationProcess and device for processing of vibration measurements of a rotating machine rotor
US6756794May 30, 2003Jun 29, 2004Bently Nevada, LlcApparatus for determining a gap between a proximity probe component and a conductive target material
US6765395May 29, 2003Jul 20, 2004Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6798194May 30, 2003Sep 28, 2004Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6819122May 29, 2003Nov 16, 2004Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6825676May 27, 2003Nov 30, 2004Bently Nevada, LlcApparatus for determining dynamic gaps between a proximity probe and a conductive target material
US6842020May 30, 2003Jan 11, 2005Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6847217May 30, 2003Jan 25, 2005Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6850077May 30, 2003Feb 1, 2005Bently Nevada, LlcMethod for measuring a characteristic of a conductive target material using a proximity probe
US6850078May 30, 2003Feb 1, 2005Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6861852Jun 3, 2003Mar 1, 2005Bently Nevada, LlcMethod for measuring a gap between a proximity probe and a conductive target material
US6904371Apr 29, 2003Jun 7, 2005Test Devices, Inc.Method and apparatus for measuring rotor unbalance
US6906532May 27, 2003Jun 14, 2005Bently Nevada, LlcMethod for digitally measuring electrical impedance
US6919731May 29, 2003Jul 19, 2005Bently Nevada, LlcMethod for measuring a position of a conductive target material
US6954062May 30, 2003Oct 11, 2005Bently Nevada, LlcApparatus for determining gaps between a proximity probe and a conductive target material
US7099782 *Jul 8, 2002Aug 29, 2006Shell Oil CompanyVibration analysis for predictive maintenance in machinery
US7539549May 25, 2001May 26, 2009Rockwell Automation Technologies, Inc.Motorized system integrated control and diagnostics using vibration, pressure, temperature, speed, and/or current analysis
US7805997Apr 21, 2008Oct 5, 2010Caterpillar IncOn-machine method for determining transmission shaft assembly quality
US8342033Jun 10, 2008Jan 1, 2013Basf SeMethod for avoiding overloading of a shaft
US8602754 *Jun 9, 2008Dec 10, 2013Baker Hughes IncorporatedSystem for monitoring an electrical submersible pump
US8958995Feb 21, 2012Feb 17, 2015Honeywell International Inc.System and method for monitoring rotating and reciprocating machinery
US9176003Feb 3, 2011Nov 3, 2015Siemens Energy, Inc.Machine vibration monitoring
US9337765 *Jan 15, 2013May 10, 2016Siemens AktiengesellschaftMethod for operating an electrical machine
US9476425 *Nov 27, 2013Oct 25, 2016Baker Hughes IncorporatedApparatus for monitoring an electrical submersible pump
US9494479Feb 7, 2014Nov 15, 2016Schenck Rotec GmbhDrive shaft balancing machine having two pedestals and first and second vibration sensors and balancing method
US20030206001 *May 29, 2003Nov 6, 2003Slates Richard D.Method for measuring a position of a conductive target material
US20030206002 *May 29, 2003Nov 6, 2003Slates Richard D.Method for measuring a gap between a proximity probe and a conductive target material
US20030206003 *Jun 3, 2003Nov 6, 2003Slates Richard D.Method for measuring a gap between a proximity probe and a conductive target material
US20030206004 *May 30, 2003Nov 6, 2003Slates Richard D.Digital eddy current proximity system: apparatus and method
US20030206005 *May 30, 2003Nov 6, 2003Slates Richard D.Apparatus for determining a gap between a proximity probe component and a conductive target material
US20030206006 *May 30, 2003Nov 6, 2003Slates Richard D.Method for measuring a gap between a proximity probe and a conductive target material
US20030210036 *May 27, 2003Nov 13, 2003Slates Richard D.Device for digitally measuring electrical impedance
US20030210039 *May 30, 2003Nov 13, 2003Slates Richard D.Method for measuring a gap between a proximity probe and a conductive target material
US20030214282 *May 30, 2003Nov 20, 2003Slates Richard D.Method for measuring a gap between a proximity probe and a conductive target material
US20030214283 *May 30, 2003Nov 20, 2003Slates Richard D.Digital eddy current proximity system: apparatus and method
US20030222639 *May 27, 2003Dec 4, 2003Slates Richard D.Determining a dynamic gaps between a proximity probe and a conductive target material
US20040034483 *Apr 29, 2003Feb 19, 2004Test Devices, Inc.Method and apparatus for measuring rotor unbalance
US20040176918 *May 27, 2003Sep 9, 2004Slates Richard D.Method for digitally measuring electrical impedance
US20040188999 *Jun 2, 2003Sep 30, 2004Samsung Gwang Ju Electronics Co., Ltd.Compressor and method of connecting pipe to the same
US20040199348 *Jul 8, 2002Oct 7, 2004Hitchcock Leith PatrickVibration analysis for predictive maintenance in machinery
US20050104579 *May 30, 2003May 19, 2005Slates Richard D.Determining gaps between a proximity probe and a conductive target material
US20090151456 *Dec 9, 2008Jun 18, 2009Baker Hughes IncorporatedDownhole tool damage detection system and method
US20090260441 *Apr 21, 2008Oct 22, 2009Caterpillar Inc.On-machine method for determining transmission shaft assembly quality
US20100171490 *Jun 10, 2008Jul 8, 2010Basf SeMethod for Avoiding Overloading of a Shaft
US20100247335 *Jun 9, 2008Sep 30, 2010Eric AthertonSystem for Monitoring an Electrical Submersible Pump
US20120330578 *Jun 22, 2011Dec 27, 2012Honeywell International Inc.Severity analysis apparatus and method for shafts of rotating machinery
US20140086765 *Nov 27, 2013Mar 27, 2014Baker Hughes IncorporatedApparatus For Monitoring An Electrical Submersible Pump
US20150022132 *Jan 15, 2013Jan 22, 2015Siemens AktiengesellschaftMethod for operating an electrical machine
CN1696630BDec 27, 2004Apr 28, 2010西北工业大Method and equipment for measuring torsional vibration of rotating mechanical rotor
CN101680739BJun 10, 2008Jun 13, 2012巴斯夫欧洲公司Method for avoiding overloading of a shaft
CN102564765A *Dec 20, 2011Jul 11, 2012浙江省电力试验研究院Method for positioning axial position of rubbing movement of steam turbine generator unit
CN102854006A *Jun 21, 2012Jan 2, 2013霍尼韦尔国际公司Severity analysis apparatus and method for shafts of rotating machinery
DE19940869B4 *Aug 27, 1999Feb 3, 2005Nsk Ltd.Vorrichtung und Verfahren zur Bewertung der Steifheit von Lagern
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WO2005083373A1 *Feb 10, 2005Sep 9, 2005Mtu Aero Engines GmbhMethod and device for identifying a shaft fracture and/or an excessive rotational speed in a gas turbine
WO2011149869A3 *May 24, 2011Sep 27, 2012Siemens Energy, Inc.Machine vibration monitoring
Classifications
U.S. Classification73/593, 73/660
International ClassificationG01H1/00
Cooperative ClassificationG01H1/003
European ClassificationG01H1/00B
Legal Events
DateCodeEventDescription
Feb 10, 1994ASAssignment
Owner name: CARL SCHENCK AG, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LIAO, MINGFU;GASCH, ROBERT;REEL/FRAME:006915/0616;SIGNING DATES FROM 19931123 TO 19940120
Dec 20, 1999FPAYFee payment
Year of fee payment: 4
Jan 10, 2002ASAssignment
Owner name: SCHENCK VIBRO GMBH, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CARL SCHENCK AG;REEL/FRAME:012463/0451
Effective date: 20000302
Jan 28, 2004REMIMaintenance fee reminder mailed
Jul 9, 2004LAPSLapse for failure to pay maintenance fees
Sep 7, 2004FPExpired due to failure to pay maintenance fee
Effective date: 20040709